In particular, in paper and pulp industry it is important to be able to measure slush consistency, because the consistency indicates the proportion of a solid in the slush. The amount and quality of the solid matter, in turn, have a crucial effect on the properties and quality of paper or board obtained as a final product.
The slush is a suspension the consistency of which may be measured by means of electromagnetic radiation, for instance. The consistency may be determined by means of the attenuation of the electromagnetic radiation, the radiation being in interaction with the suspension. The electromagnetic radiation may in that case be radio-frequency or optical radiation. The consistency may also be measured, for instance, by means of the propagation time of radio-frequency radiation. In both measurements the radio-frequency radiation or the optical radiation either goes through the suspension or reflects therefrom. Corresponding suspension measurements may also be carried out in other fields of industry.
The measurement of the amount of solid in the suspension is disturbed, however, by air or another gas present in the suspension, which gets into, or possibly, is intentionally added to the suspension in industrial processes. Hence, the measurement of the amount of solid in the suspension becomes inaccurate.